6 Answers
6

Put a "not gate" from the Pistons to the pressure plates (if you're using them). A not gate is where you make a redstone trail up to a redstone torch on a 1x1 wall. Then on the other side of the block, you make another redstone trail to directly underneath the pressure plate/whatever else you're using and (optional) one more trail on the right side of the block (redstone torch view) to directly underneath your other pressure plate.